Polyolefin materials include the following: thermoplastic polyolefins: polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1); Polyolefin elastomers (POE): polyisobutylene (PIB), ethylene propylene rubber (EPR), ethylene propylene diene monomer (M-class) rubber (EPDM rubber). Such materials, especially in a tubular configuration (i.e., tubular members), are utilized to deliver or convey an assortment of media that may have corrosive chemical properties. PE and PP tubular member is commonly used by gas utility companies, for example. Such tubular members themselves may be deployed in environments that also subject the exterior of the tubular member to corrosive or otherwise physically or chemically damaging conditions. Polyolefins are also materials from which various other types of structures, such as holding tanks, pressure vessels and the like, which may be deployed in harsh environments.
There are also various types of field connections that may be made to polyolefin tubular member. These include couplings such as tees, elbows, reducers, and so on. Field connections typically employ some form of crimping force to squeeze the joints together. This crimping process is known to introduce micro-cracks in the tubular member material. These micro-cracks can grow over time, due to cyclic pressures, exposure to temperature swings, material embrittlement, and so on, leading to failure or leaks.
Persons of ordinary skill in the art will appreciate that polyolefins are materials that by their very nature are difficult to bond to, due to their molecular density and low surface energy. This prevents most simple methods of bonding most types of materials to a polyolefin surface from being entirely effective. Consequently, there has heretofore been little that could be done to repair polyolefin structures that have become degraded by mechanisms such as described above. Tubular members may exhibit mechanical damage, including the growth of micro-cracks that can be induced from crimp connections. Of course, this is undesirable where such defects could allow for leaking, posing dangers to individuals or the environment.
When deploying polyolefin tubular member in a particular application, it is of course frequently necessary to join two sections of tubular member together end-to-end. One method of accomplishing this is by welding the tubular member sections together. In a common technique known as butt fusion, the two tubular member sections are heated by a welding plate in the form of a heated disk to cause the ends of the tubular members to become molten. The welding plate is then removed and the tubular member sections are pressed together with some predetermined force for some predetermined duration of time, depending upon wall thickness and tubular member diameter. The result is a weld joint that typically has a circumferential bead cap. There are known potential problems with such weld joints, due to stress differentials and the like that may exist in the heat-affected zone. Weld joints are susceptible to cracking over time, either due to external forces, such as soil movement or physical impact, or due to the material becoming brittle over time.